1. Field of the Invention
This disclosure is related with the field of diagnostic and interventional ultrasonography. Specifically to a pharyngeal ultrasound guide (PUG) to be placed inside the pharynx which allows the transmission of ultrasonic waves from a ultrasonic probe placed therein; the technique of acquisition of the ultrasonic images and Doppler measurements using such a device; and the procedures which may be performed using the images.
2. Description of Related Art
In physics, ultrasound refers to all acoustic energy with a frequency above the upper limit of human hearing; approximately 20,000 hertz. Typical diagnostic sonography scanners used for medical imaging operate in a frequency range of 2 to 18 megahertz, a hundred times or more greater than the limit of human hearing.
Ultrasonography (sonography) has become a widely used imaging technology in clinical medical science. While it initially was only used as a noninvasive diagnostic tool, ultrasound is now used in therapeutic procedures as well as being a visual guide in interventional procedures such as vascular access, nerve blockage, biopsies or fine needle aspirations. Ultrasound techniques have been used in different medical specialties. For example, diagnostic sonography is currently used in the fields of anesthesiology, cardiology, critical care, endocrinology, emergency medicine, gastroenterology, gynecology, obstetrics ophthalmology and urology, in addition to many other fields.
Despite its wide use across several medical disciplines, diagnostic sonography still remains an examiner-dependent procedure, requiring the knowledge of anatomy, physics of ultrasound and Doppler, functional ultrasound anatomy, and advanced invasive techniques.
In application, diagnostic sonography is based on the principle of piezoelectricity, a propriety of polarized molecules trapped within a crystal matrix. When stimulated by alternating electric current, molecules vibrate generating ultrasound. Conversely when an ultrasonic wave strikes the crystal, the resulting vibrations of polarized molecules generate alternating electric current.
Medical sonography, therefore, generally uses a probe containing one or more acoustic transducers to send strong, short pulses of ultrasound into a material, specifically different body tissues. The sound waves are partially reflected back to the transducer from the layer between body tissues with different acoustic densities, known as acoustic interface. The greater the difference between the acoustic impedances detected by the transducer, the larger the echo. However, if the pulse hits a gas-filled cavity (such as an airway or lung) or solids (such as bone), the density difference is so great that most of the acoustic energy is refracted or absorbed, distorting the image and inhibiting visualization of structures located deeper than the gas or solid impediment since the wave effectively cannot continue beyond the impediment.
Where the sound wave is reflected back, the probe detects the reflection as an echo. The echo waves vibrate the transducer and the transducer turns the vibration into electrical pulses that travel to a processor associated with the ultrasonic scanner where they are processed and transformed into an image. The time it takes to travel back to the probe is measured by the ultrasonic scanner and used to calculate the depth of tissue interface causing the echo. In addition to timing, the ultrasonic scanner also detects the strength of the echo and its focal length and uses these measurements to give the resultant image depth and clarity. Thus, structures of different density are shown as different colors, saturations, or tints. Once the scanner has determined these three things, it can create a digital image of the area being examined which can be read by one used to interpreting the different parts of the image as corresponding anatomical structures.
One of the advantages of diagnostic ultrasonography is its ability to image muscles, soft tissues, vessels, and organs very well and its particular ability for delineating the interfaces between solid and fluid-filled spaces in the body. Other advantages include that it is relatively non-invasive, renders images generally in real-time, is non-radiating, is inexpensive, is readily portable, and permits bedside evaluation.
The major disadvantages of ultrasonographic resonance technology relate to the poor image acquisition when bone or other solids, or gaseous space, exists between the transducer and the area of interest as due to the extreme differences in acoustic impedances between the gaseous and solid medium and the adjacent tissue, the area of interest is blocked from view. This often means that sonography is not useable for imaging certain structures of the body due to neighboring structures acting as blocks to the signals or that certain structures can only be imaged from certain directions.
In addition, ultrasonography is an operator-dependent technology and the images are often relatively difficult to acquire and interpret. Specifically the operator needs to understand how the densities and related images correspond to anatomical structures. As such, a high level of skill and experience is needed to acquire good quality images and make accurate diagnoses, sonography often requires additional specialized personnel to be used.
Due to its many advantages, ultrasonography is utilized in a number of different techniques the probes are often specifically designed for specific uses. Thus, there are provided, but not limited to, abdominal, pelvic, trans-vaginal, vascular, soft tissue, eye, trans-thoracic and trans-esophageal echocardiography (TEE), intra-operatory, echo-endoscopy, intravascular, and intracoronary probes. Some of these are designed for use external to the human body, while others are for internal use using natural or man made orifices to provide access.
Trans-esophageal Echocardiography (TEE) is currently used as a diagnostic and monitoring tool during the peri-operative period of cardiac and several non-cardiac surgeries as well as for certain cardiac evaluations. TEE has generally become the standard of care for cardiovascular monitoring, diagnostic and guidance in cardiac and several non-cardiac surgical and interventional procedures.
In TEE, the transducer is placed in the esophagus. Since the esophagus runs behind the heart, the echo does not have to travel through the front of the chest, avoiding obstacles such as the ribs and lungs. Thus, it often offers a much clearer image of the heart, particularly, the back structures, than does a standard cardiac echocardiogram obtained by applying a transducer to the front of the chest.
TEE provides a more complete anatomic and functional evaluation of the heart and great vessels than external endocardigraphy. Owing to its advantages, such as being relatively non-invasive, real-time and bed-side, the usefulness of TEE as a monitoring tool has spread in cardiac and non-cardiac high risk procedures. Currently the multi-plane technology of 2D images and Doppler measurements which the TEE can provide are able to analyze: heart valves, aortic and pulmonary vessels, myocardial contractility, systolic and diastolic function, intra-cardiac shunts, air embolism, pre-load, volume responsiveness, after-load, cardiac output, renal artery blood flow, hepatic venous outflow, and functioning of ventricular assistance devices.
The pharynx is a fibromuscular tube which extends from the base of the skull to the lower border of the cricoid cartilage (at which point it becomes the esophagus). Portions of the pharynx lie posterior to the nasal cavity (nasal pharynx), oral cavity (oral pharynx) and larynx (laryngeal pharynx). The inner layer of the pharynx is comprised of mucosa. The outer layer of the pharynx is comprised by a group of constrictor muscles. The pharynx communicates with the air of the atmosphere through the oral cavity and nasal cavity and serves as the airway. The inner surface of the pharynx is generally irregular due to the cavities and anatomic structures present such as: nasal cavity, palate, oral cavity, base of the tongue, tonsils, epiglottis, valecula, cartilages and the opening of the glottis. The anatomic irregularities generally prevent adequate contact and stabilization of an ultrasonic probe within the region as it is very difficult, if not impossible, to avoid a probe in the area having significant air interference from air both within, and flowing through, the pharynx. For this reason, TEE probes, while common for imaging the heart from the esophagus, have not been used in imaging structures in the pharyngeal region of the neck or throat.
A central venous catheter is a catheter placed into large vein in the neck (the internal jugular vein), chest (the subclavian vein) or the groin (the femoral vein). Central venous access is required for central venous and pulmonary artery wedge pressure monitoring and for the placement of a trans-venous cardiac pacing device. It might also be necessary for fluid infusion, blood transfusion and drug administration if a peripheral IV cannot be established. The central venous catheter insertion has associated complications such as, pneumothorax (air in the pleural space which may compress the lungs), hemothorax (blood accumulation in the pleural cavity, the body cavity that surrounds the lungs), air embolism, catheter embolization, infection, cardiac arrhythmias, cardiac tamponade and placement of the catheter in the wrong direction inside the vein. Some of these complications are severe enough to cause death.
One area in which diagnostic ultrasonography is developing is as a visual guide for central venous catheter placement to help reduce the incidence of complications such as those listed above. The ultrasound provides real-time images that are useful in the central venous catheter placement process. The incidence of complications is higher when using the blind technique compared to ultrasound guide techniques and therefore such imaging is generally a preferred process in the placement. The most common vein used to insert a catheter during cardiac surgery is the internal jugular vein, located in the neck.
As many major surgical procedures require central venous access, improved safety in the process is highly desirable. External ultrasound-guided puncture is considered state-of-the-art and standard of care for central line placement. The ultrasound surface probe that is currently employed in such guided techniques requires the use of gel on the surface of the skin to provide for clear image quality and a sterile cover sheath around the probe and its cable. In order to visualize the whole procedure including the insertion of needle, guide wire and catheter, it is necessary to use in-line technique, which means the ultrasound beam is aligned with the longitudinal axis of the vessel being imaged.
Using a surface probe in such a fashion it is necessary an additional professional to hold the probe still in the longitudinal view of the jugular vein while a wire guide is inserted through a needle as the probe must remain in the puncture area to provide real time imaging. The preparation process prior to the puncture therefore may be time-consuming and may increase the risk of bacterial contamination as the skin break, which is necessarily present in the insertion of the needle, is necessarily close to the external ultrasound device and may be in contact with the ultrasound gel used to capture the image.
Many of the problems of external ultrasound can be avoided by use of an internal ultrasound probe which can be placed within the neck prior to the procedure being performed. However, while a TEE probe is capable of being placed in the neck and passes through the neck on its way to the esophagus, a TEE probe has been generally unable to image the structures of the neck with any precision.